A prospective, interdisciplinary study is being conducted concerning immunologic response of children and adults in whom postpericardiotomy syndrome develops. Objectives are to (1) clarify pathogenesis of the syndrome, (2) learn whether there is a correlation between clinical manifestations and circulating antibodies against myocardium and certain viruses in adults as in children. (3) Develop a specific diagnostic test, (4) determine optimal management and (5) if possible, prevent the complication. Our studies on a triple-blind basis in 400 children undergoing intrapericardial procedures indicated a correlation between the presence of syndrome, which occured in 27% of subjects, and high titer of heart-reactive antibody and a fourfold or greater change in complement-fixing antibody against one or more of eight common viruses. We are expanding the study to include adults undergoing intrapericardial surgery to learn whether the same associations occur after surgery in adults as in children. We shall evaluate at prescribed intervals clinical syndrome in the patient and concurrently measured serum antibody against myocardium and 13 specific viruses. We are testing whether heart-reactive antibody can be determined by radioimmunologic as well as by immunofluorescent techniques. Cytotoxicity of heart-reactive antibody is being tested in 51Cr-labelled, cultured cardiac cells.